ICs are often sorted (binned) according to an operating parameter, such as operating speed. Operating parameters are generally characteristics of the IC that affect its performance in an application. Operating parameters can vary between wafer lots, between wafers in a wafer lot, or between parts (ICs) separated from a single wafer. In other words, there is a distribution of performance within a population of nominally identical parts.
After separating the ICs from a wafer, the parts are electrically tested on a test station. A typical test station runs a series of tests, first checking for gross failures, then running performance tests and infrared (“IR”) scanning for mechanical defects or damage that can occur during electrical testing. After testing, parts are often binned according to their test results. Gross failures can be analyzed to determine the cause and mechanism of failure. Parts that are good may vary in desirability. For example, in a population of nominally identical ICs, some will be able to operate at a higher speed. Such devices are particularly desirable in applications where high-speed ICs are used. ICs operating at a lower speed are suitable for lower-speed applications, and are typically less expensive, which is desirable for customers who don't need the highest speed parts.
Binning the parts after testing provides high-performance parts for users needing that performance, and offers lower-cost parts for users that can accept the lower performance. Without binning, high-performance customers would have to relax their specifications or accept a lower yield, and other customers would have to pay more for performance that doesn't necessarily provide an advantage for them. Binning also allows the manufacturer to make better use of the parts distribution (i.e. higher manufacturing yields).
Some parts are packaged and marked before testing. The marking often includes an identifier that makes tracking an individual part very easy. Other parts do not have markings, and look essentially identical to each other. After testing the parts, they are conventionally loaded into chip carriers (“trays”) according to their bin category at a test work station.
A conventional test work station has a bench top and shelves. The shelves contain various boxes in which the trays are placed when they are full or when binning is completed. The boxes have labels according to the bin category. However, conventional test work stations are vulnerable to mixing parts after segregation. Post-bin mixing can occur if trays of devices of a particular speed are mixed with trays of another speed, trays are placed in the wrong box, or if boxes are inadvertently mixed together.
A system for segregating ICs having different operating parameters so as to avoid post-test mixing is desirable.